Rafael Nadal showed no signs of rust in his first action in a month as the top seed easily dispatched Mischa Zverev 6-3, 6-3 at the Acapulco International on Tuesday.
Nadal, competing for the first time since falling to Novak Djokovic in the Australian Open final, has reached the final in all three previous appearances in Acapulco and now has a record of 15-1 in the event.
The World No 2 faces Nick Kyrgios in the round of 16 after the Australian defeated Andreas Seppi of Italy 6-3, 7-5.
Second seed Alexander Zverev lost just one point on serve in a dominant 6-3, 6-3 win over Alexei Popyrin while John Isner, seeded third, recorded 18 aces in a 6-3, 4-6, 6-3 win over France’s Adrian Mannarino. Isner next faces fellow American Sam Querrey, who beat Guillermo Garcia-Lopez 6-3, 6-2.
Fourth seed Diego Schwartzman needed more than two hours to advance past Marius Copil 6-3, 4-6, 6-1. Schwartzman has returned to action after a right leg injury forced him to retire at the Rio Open last week, preventing him from defending his title.
He next faces Briton Cameron Norrie, who defeated Japan’s Yoshihito Nishioka 6-2, 2-6, 6-2.
Nishikori shines on Dubai debut as seeds continue to tumble
Kei Nishikori was made to work hard by ailing Frenchman Benoit Paire before winning 6-4, 6-3 to reach the second round of the Dubai Duty Free Tennis Championships on Tuesday.
The world No 6, making his debut in Dubai, saved seven break points in the first set before taking full advantage of Paire's troublesome right knee and prevailing in 81 minutes.
"It's never easy playing Benoit. He has a great serve and a great backhand," Nishikori said.
"I think the key was the longest game at 2-1 in the first set. I was able to get the game. I was more confident. If he broke back, anything could have happened. It was a good match."
Top seed Nishikori will next take on Polish qualifier Hubert Hurkacz who beat another Frenchman in Corentin Moutet 6-3, 7-5.
The seeds continued to tumble as Daniil Medvedev and Marin Cilic crashed out in the opening round.
World No 113 Ricardas Berankis stunned eighth seed Medvedev 6-3, 6-3 while Frenchman Gael Monfils knocked out third seed and former US Open champion Cilic 6-3, 4-6, 6-0.
The Lithuanian qualifier, Berankis, who won his 11th ATP Challenger title last month in Rennes, faces Denis Kudla next after the American rallied past Matteo Berrettini 2-6, 7-5, 7-5.
Twice finalist Tomas Berdych faced a stern test from lucky loser Ilya Ivashka before prevailing 6-4, 4-6, 7-6(4) in two hours and 30 minutes.